ok, @Nevertriedoysters I am going to invent some names.
Am I right?
you were expecting to inherit a share of your parents house, but you didn't. Your sister "Sally" inherited it all.
You have sons "John" "James" and "Jack"
Your sister Sally offered to share some of her inheritance with your sons.
Your son "John" lives in your house, and intends to keep it, and is assuming his gift from his Aunt Sally is enough to pay for it, and that you agree to sell it to him, so is acting as if he is already the owner and has changed the locks.
Meanwhile, no sale has happened, no ownership transfer has taken place, and you are not sure if it will, as you don't know how much money Sally will give him, or when.
Is this right?
So you have inherited nothing from your parents at all, they willed it all to Sally, is that right?
And it would be very unlikely that Sally has inherited so much that she is able to gift her nephews the cost of a house each, even if she chose to.
And if it is her money, then she might chose not to give them anything at all.
So your son John has got it into his head that he is owed a house and is trying to take it from you forcibly?
You need to evict him. It isn't a police matter, it is a civil matter, but he needs to get out of your house
Is this where you live? Are you married? Where is your partner? Is he John's father? Have I understood the story right or completely wrong? And where are other sons James and Jack in all this?